Modern aircraft typically utilize multiple on-board electrical systems and controls during flight to ensure proper operation of the aircraft. One environmental risk aircraft are exposed to during flight is the potential of a lightning strike hitting the aircraft. When lightning strikes an aircraft, a surge of electricity passes through the aircraft and any unprotected electrical systems onboard the aircraft. The surge can overload unprotected electrical systems and damage or destroy the unprotected electrical system. This surge of electricity is referred to as a lightning transient surge. In order to protect against these lightning transient surges, aircraft include lightning protection circuits connected to one or more on board electrical systems. The lightning protection circuits shunt the lightning transient surge away from the protected electrical system, and to a neutral power line.
Some existing lightning protection circuits utilize a transient voltage suppression device as a clamping portion of the transient surge protection. Existing circuits utilizing this type of configuration do not have a way of testing the full functionality of a lightning protection circuit without removing the module containing the lightning protection circuit from the aircraft itself. As a result, the functionality of the lightning protection circuits is determined during maintenance and assumed to be maintained until the next maintenance. Verification of the functionality is then performed at the next maintenance when the module is removed from the aircraft.